The paramilitary personnel chose to conduct this just as a Miami Heat game was coming to a conclusion and traffic and people were clogging in the streets. And of course, no one knew this was only a show, and not the real thing. Again, here's the official story for the hopelessly hapless who believe it:

The training is designed to ensure that military personnel are able to operate in urban areas and to focus on preparations for overseas deployment. It also serves as a mandatory training certification requirement.

It is so un-pc to say this anymore, especially post-Sandy Hook, but, ask any self-defense enthusiast, again, why they need military-style rifles and high-capacity magazines? Reason #1 is in this blog post and often repeated all over the country. Reason #2 is this: when gangs of leeches want to come and take what you have that they don't have.